Electroexplosive devices appear in a multiplicity of sizes and configurations, and are used to detonate and initiate explosives or explosive components in ordnance. In general, electroexplosive devices, conventionally called squibs, are designed to initiate or fire at low-energy levels. A typical configuration involving an electroexplosive device consists of an electrical conductor (bridgewire), often as small as 76 mm in diameter, connected between two metallic posts. The electroexplosive device in turn is connected to an electrical circuit used to initiate the device. When the energy in the bridgewire causes it to reach a given temperature, the primary charge of the explosive device is detonated. Electroexplosive devices can be inadvertently initiated by induced current caused by electromagnetic energy. Conventional safety standards require that induced electrical currents not exceed fifteen percent of the maximum no-fire current of the bridgewire of an electroexplosive device. Maximum no-fire current is defined as the maximum current level that can be maintained in the bridgewire without causing the device to fire. In prior art devices, induced currents are measured using thermocouples disposed in close proximity to the bridgewire. Certain disadvantages result from the use of thermocouples. Thermocouples may alter thermal and electrical characteristics of the electroexplosive device. Further, electrical leads of the thermocouple may alter radio frequency characteristics of the ordnance system under test. Both of these conditions can cause inaccuracies in the measurement of the induced bridgewire currents.
Another problem identified with the use of thermocouples for measuring induced electromagnetic currents in bridgewires involves alignment problems when assembling the thermocouples to the bridgewire. Significant time and proficiency are required to assemble the bridgewire and thermocouple to attain the sensitivity necessary for detecting the presence of induced electromagnetic currents. Assembly techniques for the present invention, employing infrared optical fibers, diminish this problem.
An alternate method proposed for measuring bridgewire currents uses fluoroptic techniques. Certain problems also are encountered using this method. A problem associated with this technique is slow system response time, characteristically in the range of 70 ms. Also, thermal characteristics may be altered due to the method of sensing temperature.
A further method using a coating of wax on the bridgewire and observing changes in the wax when the bridgewire reaches a given temperature characterized by changes in the wax has also been employed. This method is crude when trying to evaluate precise bridgewire temperature versus induced magnetic currents. The wax also alters the thermal characteristics of the bridgewire.
As a result of the deficiencies in the prior art, there is a need for a new and improved means for measuring temperatures of bridgewires contained in electroexplosive devices. This new means must be capable of making measurements without altering thermal or electrical characteristics of the electroexplosive device.